Poor oral feeding with subsequent growth failure is an enormous problem for infants with congenital heart disease (CHD) because persistent growth failure is associated with higher mortality following cardiac surgery, more complications, and delayed neurodevelopment. More than a quarter of all infants with CHD and at least half of those with single ventricle disease have a feeding disorder by age 2 years. Over 50% of infants with Down syndrome (DS) have CHD, which often requires surgical intervention in the first months of life. Most infants with DS have feeding problems due to hypotonic facial, lip, and tongue muscles as well as abnormal oral cavity volume. Given the prevalence of feeding problems in infants with CHD, infants with DS who also have CHD are at especially high risk for feeding disorders that persist well into childhood. Feeding is a dynamic process affected by multiple factors, conceptualized in dynamic systems theory as constraints that are defined as boundaries or limits on the ability to coordinate a task. Feeding constraints could be supportive (e.g., prescribed protocols) or limiting (e.g., severity of infant disease). The overall long-term goal of this research of infants with DS and CHD is to develop interventions to support and enhance oral feeding. The primary purposes of the parent study are to comprehensively characterize oral feeding dynamics during the newborn hospitalization in infants undergoing operative intervention for CCHD in the first month of life and identify the relationships among feeding constraints, oral feeding dynamics, and feeding-related outcomes. This supplement will add the high risk group of infants with DS to the population studied. Oral feeding dynamics (readiness to feed, behavioral and physiologic response) will be measured using the Early Feeding Skills (EFS) assessment tool for an overall assessment and the dynamic-EFS for a second-by-second analysis of videotaped feedings for relationships between behavior and physiologic response. Physiologic response will include continuous measures of heart rate, respiratory rate, oxygen saturation, and heart rate variability. Task constraints will be measured by type of milk consumed (breast milk or formula). All infants will be bottle fed, standard for most infants with CHD, and rate of milk flow will be adjusted to each individual infant. External constraints will be measured with unit feeding guidelines and prescribed feeding protocols. Internal constraints will be measured by infant severity of disease and age at surgery. Outcomes will be measured for individual feedings using measures of feeding performance including total intake, proficiency (percentage of prescribed intake), efficiency (rate of milk intake), and feeding duration. Outcomes at discharge will include feeding milestones, growth, use of occupational therapy services, tube feeding at discharge, and length of stay. Knowledge of the unique characteristics of feeding infants with DS and CHD will inform and enable development of interventions tailored to specific capacities for feeding, thus promoting the health and wellbeing of these vulnerable infants through reducing morbidity and mortality and optimizing neurodevelopment.